SUMMARY To determine whether postural changes in ratio of upper to lower (U:L) zone pulmonary blood flow reflect pulmonary arterial pressures, we used pulmonary perfusion photoscintigraphy to study 12 normal subjects and 10 patients with precapillary pulmonary hypertension (eight classified as "primary" and two as thromboembolic). All patients underwent right-heart catheterization and measurement of pulmonary arterial systolic, diastolic, mean and capillary (wedge) pressures. The distribution of perfusion -was t-hen assessed in the supine and erect positions after i.v. injection of technetium-99m-labeled, macroaggregated atbumin. Perfusion distribution was corrected for lung volume by xenon-133 equilibrium ventilation scans. In normal subjects, the U:L lung zone perfusion ratio decreased by 70.7 + 12.2% with the change in position. The patient group differed (p < 0.0001) from normal subjects in that there was only a 19 + 17.4% shift of U:L ratio with the postural change. The mean pulmonary arterial pressure in the patient groups was 50 ± 24.2 mm Hg. The postural change in U:L zone ratio correlated significantly with the mean pulmonary arterial pressure (r = -0.84, p < 0.01) pulmonary arterial systolic (r = -0.83, p < 0.01) and diastolic pressures (r = -0.72, p < 0.05) and with the pulmonary vascular resistance (r = -0.74, p < 0.02). No correlation was found with other hemodynamic, spirometric or blood gas data. We conclude that the postural shift in U:L ratio warrants further exploration as a noninvasive approach for detecting and quantifying pulmonary hypertension.A NONINVASIVE method for detecting and quantitating pulmonary arterial' hypertension would be useful in many investigational and clinical contexts. Several promising methods are being explored,'`but none has provided consistently useful results. We investigated the value of a method that relies on detecting the alteration in the apex-to-base distribution of pulmonary blood flow that occurs when patients move from the supine to the erect position.The apex-to-base distribution of pulmonary blood flow is normally determined by the relationships among pulmonary arterial, pulmonary alveolar and pulmonary venous pressures. In the erect position with normal pulmonary arterial pressures, these relationships, modulated by gravitational hydrostatic effects, result in an increment in flow per unit lung volume fro-m the apex--to the base of the lung. In the supine position, the apex-to-base distribution is much more uniform because the longitudinal axis is perpendicular to the gravitational hydrostatic effects.Under normal-circumstances, a substantial shift in the distribution of pulmonary blood flow can be anticipated when a person moves from the supine to the erect position. If pulmonary arterial pressure is significantly elevated and pulmonary alveolar and venous pressure are not significantly altered, a different apex-to-base perfusion pattern-might be anticipated. In patients with pulmonary arterial hypertension, the apex-to-base distribution should be subst...

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